(a) Field of the Invention
The present invention relates to a pulse shaping method. Particularly, the present invention relates to a pulse shaping method with a finite time interval.
(b) Description of the Related Art
In general, a communication system uses a band-limited pulse so as to control the bandwidth of transmitted signals. The band-limited pulse, generally referred to as a Nyquist pulse, controls a signal that has a finite bandwidth and that is sampled by accurate symbol timing to not have inter-symbol interference (ISI). The most widely used Nyquist pulse is the raised-cosine (RC) pulse.
However, the Nyquist pulse is not the only one. That is, other types of Nyquist pulses as well as the RC pulse can exist. The Nyquist pulse has no ISI when symbol timing is accurate, and the Nyquist pulse has ISI when the symbol timing has an error. Recently, pulses with ISI of less than the RC pulse while having a symbol timing error have been proposed.
Since the Nyquist pulse has a finite bandwidth, the length of the pulse in the time domain becomes infinite. However, it is impossible for the actual transmitting/receiving system to realize a pulse with an infinite length in the time domain. Generally, in the communication system, the Nyquist pulse is divided into a transmit pulse and a receive filter response, and the transmit pulse and the receive filter response are cut to a predetermined length to be used in the time domain. That is, in further detail, a pulse with a finite time interval used in a real communication system is no longer a Nyquist pulse.
Relative performance of the pulses is variable by the length of the time domain. That is, the pulse A outperforms the pulse B in consideration of a long pulse existing interval (the transmit pulse and the receive filter response are cut so that they may maintain the long interval in the time domain), and the pulse A may have worse performance than the pulse B when they are cut more shortly (i.e., the transmit pulse and the receive filter response of each pulse are cut to maintain short intervals in the time domain).
Therefore, the conventional method of cutting, in the time domain, the square-root Nyquist pulse (its square root becomes the Nyquist pulse in the frequency domain) which is infinitely long in the time domain and using the same may not maintain relatively better performance in the case of the Nyquist pulse. That is, the cutting of the pulse in the time domain cannot guarantee relatively better performance of the original pulse.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.